The increasing technological development stimulates and challenges the evolutive progress of society, thus enlarging the capacity of storage, processing and transformation of the information into knowledge. Such fact is observed in view of the necessity of innovating whenever we face a certain obstacle and/or problem, it requiring an effective solution which unites rapidity, objectivity, productivity and an excellent cost/benefit relation.
The use of metallic packages for the storage of various products is generalized practice, specially in relation to the packages of food, beverages and other applications in general that are retailed. These packages shall have a distinctive look presentation in order to attract the consumer's attention, helping him, at the same time, in the selection of the desired product. The resource nowadays adopted to reach such objectives consists of printing labels in several colors, directly on the metallic surface of these packages. Therefore, there were developed inks and automatized specific processes, which allow a production volume of the order of million of units per day.
One such process and related equipment is described by Rush in U.S. Pat. No. 3,960,073 “Machine for decorating two-piece cans”, in which a sequence of operations are performed at a plurality of work stations fixed about the outer circumference of a vertically arranged supporting indexing table. The cans are conveyed to the machine and inserted on mandrels which are arranged around the rim of said indexing table. The mandrels holding the cans rotate about their individual axes, and the table is rotated in discrete forward and stop motions, which bring the cans to a plurality of work stations where they are coated with a base coating of UV-polymerizable plastic resin followed by several printing stations in which different coloured resins are applied by means of a offset printing process. Between said stations, the cans are brought in front of ultra-violet dryer stations, where the UV radiation polymerizes and cures the several layers of plastic resin.
Such printing techniques present satisfactory results in almost all cases. However, the high production volume—which, in the case of drink cans, can reach 6 million units per day—causes even a relatively low percentage of inappropriate printings to result in a considerable volume of waste, in absolute terms. Upon considering the losses that occur during the adjustment of the printing equipment, the number of rejected units is of the order of 1,000,000 per month.
Upon considering that, in the case of the drink cans, the body weighs about 12 grams, the waste estimate can reach 18 tons per month of aluminum, of which recycling is imposed due to the value of this metal. Traditionally, this recycling has been carried out by returning the cans as scrap to the aluminum works, wherein the material is casted and reused. Nevertheless, the casting process consumes electric energy which can be harmful to environment. From the point of view of the industries that produce these packages, it is further necessary to consider the charges arising from the administrative expenses and the material conveying costs.
The removal of the ink from the cans is, therefore, a recommendable alternative, it making the operation of the industries involved in the process more profitable. However, the removal by organic solvents presents a negative impact to the environment, and it can cause penalties such as fine up to a possible interdiction of the operations. On the other hand, the printing process requires the application of the ink onto a flat surface, thereby making impracticable the techniques of ink removal by means of abrasion. Moreover, in processes comprising the polymerization between stations in which ink is applied—such as described in U.S. Pat. No. 3,960,073—removal by solvent becomes unfeasible. Therefore, many plants do not use the printing process described above. Rather, the curing step is performed in a separate machine or oven, coming after all the printing steps have been performed. Between the end of the ink applying process and the curing oven the quality of the printing can be verified and the misprinted cans may be diverted to a printing-removal device, the operation of which preserves the polished surface of the cans which can thereafter be returned to the production line.